The present invention relates to a silver halide emulsion having a high sensitivity and an improved pressure property, and a silver halide photographic material using the same.
Manufacturing methods and use techniques of tabular silver halide grains are disclosed in U.S. Pat. Nos. 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306, and 4,459,353. Known advantages of tabular grains are, e.g., improvements of the sensitivity/graininess relationship, including improvements of the color sensitization efficiency obtained by spectral sensitizing dyes.
Various studies have been made to improve the properties of tabular grains having such advantages.
U.S. Pat. No. 5,219,720 has disclosed a technique of improving the sensitivity/graininess ratio by decreasing the distance between twin planes of a tabular grain having (111) faces as major surfaces.
Jpn. Pat. Appln. KOKAI Publication No. (hereafter referred to as JP-A-)6-273869 has disclosed a technique of improving the manufacturing stability by using low-molecular-weight gelatin in a nucleation step in the formation of tabular grains.
On the other hand, demands for resistance to pressure of a silver halide emulsion is becoming stronger than before as the silver halide emulsion becomes to have a higher sensitivity. Generally, it is known that as various pressures are imposed to a silver halide photosensitive material, the photographic property thereof changes. For example, when a pressure is imposed to a silver halide photosensitive material during the manufacture thereof or during conveyance thereof in a camera, or the photographic material is bended, fogging arises or sensitivity decreases, which is a problem of a practical use. Especially, when a photosensitive material is bended, the bigger the equivalent-circle diameter and thinner the thickness of a tabular grain, the easier to occur fogging and reduced sensitivity. Accordingly, it was desired for such grains to both heighten the sensitivity and improve the pressure resistance.
Techniques to introduce dislocation lines with high density and to limit the position of the dislocation lines, and making distribution of silver iodide content between grains uniformly, are disclosed, for example, JP-A-6-27564 and JP-6-258745. Further, a technique to control the (100) surface area ratio to all the surface area of a tabular grain is disclosed, for example, in JP-A's-2-298935 and 8-334850.
However, there is no description in these patent applications of the use of an emulsion containing grains having a large equivalent-circle diameter and a thinner grain thickness, having a high (100) surface ratio to all the surface areas, and having high density dislocation lines introduced at a fringe portion of the grains, and in addition, the distribution of the silver iodide content between the grains is uniform.
Also, JP-A-8-95181 has disclosed a technique of increasing the sensitivity in a small-size region. However, a technique of increasing the sensitivity of tabular silver halide grains in a large-size region, which aims to achieve high sensitivity that is important in the competition with digital cameras in the future, is still immature. Hence, a technique of increasing the sensitivity has been desired.